Wide angle objective



f )Q 1We 7C Mrch 6, 1962 c. SANDBACK 3,023,672

n WIDE ANGLE OBJECTIVE Filed Oct. 9, 1958 2 Sheets-Sheet 1 F E? j M ai'ch 6, 1962 l. c. SANDBACK 3,023,672

WIDE ANGLE OBJECTIVE Filed Oct. 9, 1958 2 Sheets-Sheet 2 United States Patent O 3,023,672 WIDE ANGLE OBJECTIVE Irving C. Sandback, Morton Grove, lll., assignor to Bell & Howell Company, Chicago, Ill., a corporation of Illinois Filed Oct. 9, 1958, Ser. No. 766,251 5 Claims. (Cl. 88-57) This invention relates to a wide angle objective, and more particularly -to a wide angle photographic objective of the inverted telephoto type highly corrected for all aberrations.

An object of the invention is to provide a wide angle objective having a long back focal length -and highly corrected for astigmatism, chromatic variation of astigmatism and distortion as well as for the other optical aberrations.

Another object of the invention is to provide a new and improved inverted telephoto objective having a negative power group of elements positioned a substantial distance in front of the stop and a positive power group of elements closely following the stop and having a long back focal length.

A further object of the invention is to provide a wide angle objective having ve components of which the rst is a convex-plano positive singlet of extra dense lbarium ilint glass, the second a negative meniscus of barium int glass and forming a negative group positioned substantially ahead of the stop, the third is a positive meniscus singlet behind -the stop, the fourth a compound positive doublet and the fifth a positive member of either singlet or doublet form.

It is to be understood that the terms front and rear as herein used refer to the ends of the objective respectively nearer -the longer and shorter conjugates thereof.

In the drawings, FIGS. l and 2 are longitudinal sections illustrating objectives forming two embodiments of the invention.

The invention provides a wide angle objective of the inverted telephoto type including a negative front group of components spaced substantially in front of a stop and a positive rear group of components spaced closely behind the stop. Proceeding from the lfront to rear the front group includes a front convex plano singlet of extra dense barium flint glass and a rear negative meniscus singlet of barium flint glass concave to the stop. The rear group of components includes a front positive meniscus component concave to the stop, an intermediate biconvex compound doublet and a rear positive component which may |be a convex-substantially plano compound doublet convex to the stop or a convex-plano singlet convex to the stop.

Referring to FIG. 1 of the drawings, the objective shown therein includes components 1 to 5 having lenses L1 to L7, radii of curvature of the surfaces R1 to R12, axial Ithicknesses t1 to t7 and axial separations s1 to s4. The components 1 and 2 are closely spaced and form a negative group positioned a substantial distance .95 in front of stop 6 with the components most convex toward incident light. The front group of components 1 and 2 is formed of two lenses for chromatic correction. To

substantially completely eliminate Ihigher order aberrations of chromatic astigmatism and distortion, the surfaces R1, R3 and R4 are strongly convex to the incident light and the lens L1 must be of extra dense barium int glass and the lens L2 must 4be of barium flint glass having an Abbe dispersion number of not greater than about 50 and not less than about 40. Also, the surface R2 must not be strongly convex and preferably is plano or slightly concave.

The components 3 to 5 are closely spaced to one anice other and are spaced a short distance s6 behind the stop 6. The front component 3 ofthe rearv group is a positive meniscus singlet concave toward the stop, the intermediate component 4 a positive cemented or -air spaced doublet L4 and L5 with its optical surfaces as concave to the stop as possible. The rear component 5 is composed of a cemented or air spaced doublet having convex front lens L5 and a meniscus rear lens L7.

To highly correct astigmatism and distortion for half angle fields to view of 30 and greater and to minimize variation of astigmatism and distortion over such fields of view, the lens L1 is constructed of extra dense barium int glass with an Abbe dispersion number which is from l0 to 25 greater than that of the lens L1. Preferably, the lens L, has an Abbe dispersion number not greater than about 50 and not less than about 40. The optical surfaces of the lens L1 and L2 are positioned to `be highly convex to incident light which, as shown in the drawings, is from the left.

The positive rear group of elements 3, 4 and Svare spaced very closely together with the surfaces R5, R6, R7, R9 and R10 being so curved that the deviations of the light rays passing therethrough from the stop are very small. Thus, the surfaces R5 and R6 are concave to the stop as the light path is expanding from the stop. The surface -Rq is convex to the stop and receives the light rays converging somewhat from the lens L3, and the surface R10 also is convex to the stop to receive the converging rays with minimum deviations from perpendiculars t0 the surface R10 also is convex to the stop to receive the converging rays with minimum deviations from perpendiculars to the surfaces R10,

For high correction the objective should comply with the following inequalities in which F is the equivalent focal length thereof, and f1 to f5 are the focal lengths of the respective components 1 to 5:

A preferred example of the objective shown in FIG. 1 complies substantially with the following table in which dimensions are-- in terms of inches, nd designates the respective indices of refraction for the sodium D line and V the Abbe dispersion numbers:

5 the Abbe dispersion numbers:

Example l Example II [Equivalent local length=.496 Back focal lengthws [Equivalent focal length=.496 Back focal length=.686

pel'lllr //1-7} Aperture f/ 1.7]

R, =+1.s5s 10 Rii= -l-Lsss Li t1= .1.5 nd=i.72o V=29.a L R=P1ano tn= .175 nd=1.72o V=29.o R :Plano 025 L 13: Hggs in: i 611 V 45 o s Ri= 1.500 l n H 53:' 320 nd y L: R 3805 i til .150 nd=1.(i11 V=45.0 wf

si= .82o 15 RF. 1 000 "F S= 282 Lia Ril= .862 tn= .306 nd=1.734 v=51.2 S2= 1.102 S13= .005 R, =-1.144 Ri1= +1.520 L: R 950 ta= .330 nd=1.734 v=51.2 n Ris= .464 n= .ggg Inpgg sigg 0 is is= i= s .00s R 1.333 R1 =+L559 l 20 Rig= i .951 si4= .005 L4 R 4H t4= .225 nd=1.657 V=51.0 Liq Rni=Pla110 li|=l .100 I1d=1.517 V=64.5

s i L| Rox-1.664 .060 11.11.720 V=29.3

R +1110 s= .005 Example III [Equivalent focal length=.500 Back focal length=.718 ali- 1.110 E d Le E 47: 25 Aperture 171.7]

Ria=Plano RIU: +1440 Lii Rl *+28 628 tii= .232 l1a=1.720 V=29.3 The objective shown in FIG. 2 is generally similar to la s.,- .oio that shown in FIG. 1 with the exception that the rear 30 L R1" +1498 tn: 156 n $1.812 V=45|0 component 15 is a convex plano singlet. The objective Rn== +.3796 shown in FIG. 2 includes components 11 to 15 having :ggg lenses Ln to L16, radii of curvature of the optical sursii=1.oso faces Ru to R21, axial thicknesses su to s14 and axial L" Rl L00 tu: .316 nd=197 V=56-2 separations s15 and sie from a stop 16. For high correc- 35 Rn= .862 tion, the objective shown in FIG. 2 should conform to RU: H520 su: '005 the following inequalities, wherein F is the equivalent Ln 64 t1i= .25o ns=12o V=6o.o focal length of the objective and fu to f15 correspond t0 L.; R18: *A ti5= .08o nd=i.12o v=29.a the respective focal lengths of the components 11 to 15. Rn- 1.a4o s 005 R 5 1 26F R'11 3-6F v L1. 9 o tu .16o nd=1.511 vxem v Rzi=Plano -.025 1 .05

l n F R l F While the invention is thus described, it is not wished R to be limited to the precise details described, as changes .2 R 3 may be readily made without departing from the spirit of 13 the invention. .6F Ri4 .9F What is claimed is:

1. In an inverted telephoto lens system, proceeding 2 R14 3 50 from front to rear, a front convex-plano component con- Ru vex to the front of extra dense barium int glass, a second negative meniscus component of barium flint glass and 1.6i' R1 2-2F positioned closely behind the front component and con- R vex to the front, a stop a positive meniscus component .75 -15 .9 55 concave forward y, a compound positive component, and R a rear positive component and being further characterized F inC that the lens system is constructed in substantial com- 2 9F Rn 3 7 pliance with the following inequalities in which proceeding R1, from front to rear R1 and R3 designate the respective radii 6 s 1'3 60 of curvature of the front surfaces of the front and second components, R2 the radius of the rear surface of the 1.8F R 2.3F front component, R4 the radius of the rear surface of the second component, R5 and Re the radii of the front and 1.6F R2o 2-5F rear surfaces of the third component, R7, R8, and R9 the radii of the front inner and rear surfaces of the fourth 025 l 025 component and R10 and R12 the lfront and rear radii of F R21 F the rear component, and F is the equivalent focal length f the lens system: a.4F f 4.6F 1 4F fu 2 0F 70 2.6F R1 3.6F .025 1 .05 7.5F f|s 10.511' T R 2 F 2,3F f14 3.2F R4 2 .3 3.2F fi 4.4iF a 2. In an inverted telephoto lens system, proceeding front front to rear, a front convex-plano component convex to the front of extra dense barium int glass, a second negative meniscus component positioned closely behind the front component and convexto the front, a stop, a positive meniscus third component concave forwardly, a compound positive fourth component, and a rear positive component and being further characterized in that the lens system is constructed in substantial compliance with the following inequalities in which proceeding from front to rear R11 and R13 designate the respective radii of curvature of front surfaces of the front and second components, R12 the radius of curvature of the rear surface of the front component, R14 the radius of the rear surface of the second component, R15 and R16 the radii of the front and rear surfaces of the third component, R17, R18 and R19 the radii ofthe front, inner and rear surfaces of the fourth component, and R20 and R21 the radii of curvature of the front and rear surfaces of the rear component, and F is the equivalent focal length of the lens system:

3. In a wide angle objective, proceeding from front to rear, a front positive singlet, a second negative meniscus singlet, a stop, -a third positive meniscus singlet, a fourth compound positive doublet, and a rear positive compound doublet, and further characterized in that the objective complies substantially with the following table in which dimensions are in terms of inches and proceeding from front to rear L1 to L7 designate the lenses, R1 to R11 the radii of curvature of the surfaces, t1 to t1 the `axial thicknesses, s1 to s1 the axial separations of the lenses, nd the refractive indices of refraction for the sodium D line and V the Abbe dispersion numbers:

` [Equivalent focal length=A96 Back focal length-.686 Aperture //1.7]

4. In a wide angle objective, proceeding from front to rear, a front positive singlet, a negative meniscus singlet, a stop, a positive meniscus singlet, a compound positive doublet, and a rear positive singlet, and further characterized -in that the objective complies substantially with the following table in which dimensions are in terms of inches and proceeding from front to rear L11 to L18 designate the lenses, R11 to R21 the radii of curvature of the surfaces, r11 to tw the axial thicknesses, S11 to S11 the axial separations of the lenses, nd the refractive indices of refraction for the sodium D line and V the Abbe dispersion numbers:

[Equivalent focal length=.496 Back focal length=.686

Aperture f/1.7]

5. In a wide angle objective, proceeding from front to rear, a front positive singlet, a negative meniscus singlet, a stop, a positive meniscus singlet, a compound positive doublet, and a rear positive singlet, and 'further characterized in that the objective complies substantially with the vfollowing table inwhich dimensions are in terms of inches and proceeding from front to rear L1 to L, designate the lenses, R'11 to R11 the radii of curvature of the surfaces, 111 to t1@ the axial thicknesses, s11 to s1.1-theaxial separations of the lenses, n.1 the refractive indices of refraction for the sodium D line and V the Abbe dispersion numbers:

Back focal length: .718

nal-1.517

References Cited in the le of this patent UNITED STATES PATENTS Kitroser Feb. 14, 1933 Lee Apr. 17, 1934 Merte Aug. 9, 1938 Hopkins et a1. Apr. 22, 1952 Hopkins etal Apr. 22, 1952 Angenieux Aug. 18, 1953 Angeneux Dec. 14, 1954 Zollner et al May 28, 1957 Lautenbacher et a1 Ian. 28, 1958 Lange Mar. 11, 1958 

